Reading a Ruby in Poor Light

The first ruby I overpaid for was shown to me under a tungsten lamp in Chanthaburi. The stone read a full grade better than it was. The lesson cost me four thousand dollars, and it was cheap at the price.

Warm light flatters red stones. Burmese ruby fluoresces, and an incandescent bulb wakes that fluorescence while hiding the brown a trained eye would catch in daylight. A seller who controls the light controls the first impression. The first impression is where the seller sets his price.

So, the rule: I do not judge color in the seller’s light, ever. It costs nothing to carry the light with you, and it changes the conversation the moment the torch comes out. The serious sellers nod. They would do the same at my table.

The torch settles arguments about light. The master stones settle arguments about memory. Color memory is a myth, mine included. A ruby held beside a graded master tells the truth in about four seconds. A ruby judged against the ruby you remember from last month tells you a story, and stories are expensive.

Poor light also hides windows. Tilt the stone slowly through the beam and watch the return. A well-cut ruby holds its color as it moves. A windowed one goes glassy in the middle, and a warm lamp fills that hole with borrowed fire. Daylight leaves it empty, which is what your client will see at lunch.

When I can, I walk outside. Northern daylight at midday remains the reference standard of the colored stone trade, and it is free. In a market town nobody is surprised. In a Bangkok office tower it raises eyebrows, and I go anyway. The elevator ride has saved me more money than any instrument I own.

What the lamp is doing

An incandescent bulb burns at something under three thousand kelvin. Its light is heavy in red and thin in blue, so a red stone under it is being fed the colour it is being judged on. Brown, which is red with grey in it, disappears because the grey has nothing to show against. And a Burmese ruby, whose chromium adds light of its own, glows harder under a lamp that flatters it. None of this is dishonest in itself; every showroom in the world is lit to sell what is in it. It becomes dishonest when the buyer mistakes the lamp for the stone.

Daylight at 5500 K has the blue in it. Under that light the brown shows, the grey shows, the window shows, and the fluorescence is what it is rather than what the bulb makes it. That is the whole reason to carry the torch.

The four-second method

Stone on white paper. Torch on. Master beside it, the closest one on the scale. Look for four seconds, not forty; the eye tires and starts to argue. Then tilt the stone slowly through the beam and watch whether the colour holds or goes glassy in the middle. Then hold it at arm’s length and, if the room allows, walk to the other side of it: colour that survives three metres is colour, and colour that needs the loupe is a description. Then, and only then, listen to the story.

What the torch costs the seller

Nothing, and that is the point. A serious seller has his own masters and his own daylight and will nod when yours come out, because he would do the same at my table. The seller who objects to the torch has told you what his stone looks like in it. I have never lost a good stone by insisting on my own light. I have lost several bad ones, at prices I would have regretted.

Buy the stone you saw in your own light. If it needs the back room to look right, you have learned something important about the stone, and about the room.

Questions collectors ask

What light is best for judging a gemstone’s colour?

Daylight at around 5500 K, ideally northern daylight at midday, which remains the reference of the coloured stone trade. A daylight torch of that temperature carried to the table is the practical substitute, and it costs nothing to bring.

What are master stones?

A row of graded reference stones of one species, kept for comparison. A ruby held beside a master tells the truth in about four seconds; a ruby judged against the stone you remember from last month tells you a story. Colour memory is a myth, and masters replace it.

Why do gem sellers use warm lamps?

Because warm incandescent light is rich in red and poor in blue. It feeds a red stone, hides the brown a trained eye catches in daylight, and wakes the fluorescence of Burmese material. The seller who controls the light controls the first impression, and the first impression is where the price is set.